Electric fuse terminals



Dec. 7, 1965 p. c. HITCHCOCK ELECTRIC FUSE TERMINALS 3 Sheets-Sheet 1 Filed Nov. 2, 1962 fawwm .PauZ 6.111330054000313,

f/Iffiaflneg Dec. 7, 1965 P. c. HITCHCOCK 3,222,432

ELECTRIC FUSE TERMINALS Filed Nov. 2, 1962 3 Sheets-Sheet 2 1 7. m, a a E Dec. 7, 1965 P. c. HITCHCOCK 3,222,482

ELECTRIC FUSE TERMINALS Filed Nov. 2, 1962 3 Sheets-Sheet 3 1820982202 PauZ al'iiiciaoooffi,

.9 MM RAM United States Patent 3,222,482 ELECTRIC FUSE TERMINALS Paul C. Hitchcock, Plum Island, Mass., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Nov. 2, 1962, Ser. No. 234,963 6 Claims. (Cl. 200-132) This invention relates to electric fuses and to a process for manufacturing electric fuses.

Electric fuses include generally a tubular casing of insulating material which is closed on both ends thereof by terminal caps or ferrules. Fuses having a relatively small current rating are placed into fuse holders adapted to engage the aforementioned terminal caps or ferrules. Fuses having a relatively high current rating are placed into fuse holders adapted to engage a pair of knife blade contacts, each of said pair of knife blade contacts being integral with one of a pair of terminal caps or ferrules. This invention is concerned with fuses having terminal caps or ferrules including a knife blade contact forming an integral part thereof.

Terminal caps or ferrules are generally made of relatively thin sheet metal formed to have the shape of a cap, i.e., to include a lateral cylindrical surface and a fiat end surface. Knife blade contacts are generally stampings made of copper bars which are considerably thicker than the metal of which the terminal caps or ferrules are formed. The knife blade contacts are generally rectangular, and the cross-section thereof is also generally rectangular. One of the narrow edges of a knife blade contact must be secured to the flat end surface of a terminal cap to form an integral unit adapted to be mounted on one of the ends of the tubular casing of an electric fuse.

The process of attaching the knife blade contacts to the terminal caps or ferrules of an electric fuse to integrate both parts in the aforementioned manner into a selfcontained structural unit, or sub-assembly, involves certain difiiculties which have not been overcome heretofore.

It is, therefore, one object of the invention to provide improved terminal structures for electric fuses comprising a cap, and a knife blade contact integral with the cap.

Another object of this invention is to provide improved integral terminal caps and knife blade contacts forming self-contained structural units or sub-assemblies adapted to be readily mounted upon the casings of electric fuses.

Generally knife blade contacts are brazed to the end surfaces of terminal caps. Such a brazing operation calls for expensive jigs, requires a relatively large amount of skill if performed manually, tends to result in a non-uniform product, and is generally accompanied by annealing of the knife blade contacts, which is highly undesirable.

It is, therefore, another object of the invention to provide sub-assemblies comprising terminal caps and integral knife blade contacts which sub-assemblies can be manufactured without the drawbacks and limitations to which the aforementioned prior art brazing processes are subject.

It is possible to combine terminal caps and knife blade contacts by providing the end surfaces of the former with apertures and by providing the edge zones of the latter with projections which are inserted into the aforementioned apertures and thereafter upset in the fashion of the shank of a rivet. This rivetting process can only be successfully performed if the thickness of the cap is excessive,

3,222,482 Patented Dec. 7, 1965 and this rivetting process is not satisfactory where relatively thin sheet metal is used for forming the caps, e.g., sheet metal having a thickness in the order of of an inch.

It is, therefore, another object of this invention to provide improved sub-assemblies comprising terminal caps and integral knife blade contacts wherein the terminal caps are formed of relatively thin sheet metal.

Another object of this invention is to provide improved sub-assemblies comprising terminal caps and knife blade contacts integral with the caps which are not subject to the limitations and disadvantages of composite cap and blade contact structures formed by conventional brazing and/ or rivetting processes.

Further objects and advantages of the invention will become apparent as this description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawings wherein:

FIGURE 1 is a front elevation of an electric fuse embodying the invention;

FIG. 2 is a side elevation of the structure shown in FIG. I seen in the direction of the arrow R of FIG. 1;

FIG. 3 shows in side elevation a detail of the structure shown in FIG. 1;

FIG. 4 is a front elevation of one end of the casing of the structure shown in FIG. 1 and a front elevation of the subassembly unit including a terminal cap and a knife blade contact prior to mounting said sub-assembly unit upon the casing of the fuse;

FIGS. 5a and 5b are a front view and a top plan view, respectively, of the knife blade contact as such produced by a stamping, blanking or chopping operation;

FIGS. 6a and 6b show the same part as shown in FIGS. 5a and 5b upon having been upset or widened by a pointed upsetting tool or mandrel;

FIG. 7a is a vertical section along 7a7a of FIG. 7b and shows a terminal cap or ferrule made of a relatively thin sheet metal and being provided with an oblong hole or aperture in the end surface thereof, FIG. 7b showing in bottom view the same terminal cap as FIG. 7a;

FIG. 8a is a section along 8a-8a of FIG. 8b and shows the knife blade contact of FIGS. 6a and 6b upon having been mechanically joined to the ferrule or terminal cap of FIGS. 7a and 7b, and FIG. 8b is a bottom plan view of the sub-assembly shown in FIG. 8a;

FIGS 9a and 9b are a front view and a top plan view, respectively, of the sub-assembly shown in FIGS. 8a and 8b upon having been provided with a so-called brazing pre-form;

FIG. 10 is a diagrammatic representation of the swaging process by which the terminal cap and the knife blade contact are joined together into a self-sustained structural unit;

FIG. 11a illustrates a jig or fixture for performing a brazing process for establishing a current path of low resistance between the knife blade contact and the terminal cap and shows also how the knife blade contact is being brazed to the terminal cap, and FIG. 11b is a tor)1 plan view of the jig or fixture illustrated in FIG. 11a; an

FIG. 12 is a side elevation of a gang upsetting tool or of a two-pronged tool for upsetting blade contacts.

Referring now to the drawings, and more particularly to FIGS. 1 to 4 thereof, numeral 1 has been applied to indicate a tubular casing of insulating material closed on both ends by terminal caps, or ferrules 2. Blade contacts 3 form integral parts of caps 2 as will be shown below more in detail. Fuse link 4 is made of a metal having a relatively high fusing point such as silver or copper and is arranged inside of casing 1 and conductively interconnects caps 2 on the ends of casing 1. The preponderant portion of the entire length of link 4 is substantially in the shape of a prism, triangular in cross-section, as can best be seen in FIG. 3. Each panel of link 4 is provided with an indexed tab 4a bent over one of the rims of easing 1 to the outside of easing 1. This has been clearly shown in FIG. 3. Fuse link 4 is provided with four transverse lines of perforations 4b, and an overlay 4c of a metal having a relatively low fusing point, e.g. tin, is arranged immediately adjacent the line of perforations in the center region of casing 1. The object of overlay 4c is to initiate interruption of an overloaded circuit on occurrance of relatively small protracted overloads. The particular geometry of overlay 40 which I prefer is more fully disclosed in U.S. Patent 2,988,620 to Frederick J. Kozacka, Time-Lag Fuses, June 13, 1961, and reference may be had to that patent for additional details in regard to the preferred position of overlay 40 on link 4. The theory underlying the geometry of the particular .fuse link shown in FIGS. 1-4 is more fully described in the copending patent application of Frederick J. Kozacka, Ser. No. 185,618, filed April 6, 1962 for Springless Time-Lag Fuses for Motor Circuits, now U.S. Patent 3,143,615. The axially inner ends of ferrules or terminal caps 2 are crimped as indicated at 2a and a pair of pins project transversely through the cylindrical lateral surface of each terminal cap into casing 1, thus firmly securing caps 2 to casing 1. Casing 1 is preferably filled with a pulverulent arc-quenching filler such as, for instance, quartz sand.

The right side of FIG. 4 indicates how the sub-assembly 2, 3 comprising a cap 2 and a knife blade contact 3 is to be monted on casing 1, establishing a pressure contact between the portions of tabs 4a situated on the outside of casing 1 and the inner surfaces of terminal caps 2. It is desirable to establish a solder joint at the point of engagement between each tab 4a and one of the two terminal caps 1. to minimize the resistance of the current path through the fuse, these solder joints not having been shown in the drawings.

FIGS. 5a to 11a illustrate the various steps in the process of manufacturing the sub-assembly shown at the right of FIG. 4. The first step may consist in chopping from a relatively long copper bar relatively short sections to be used as knife blade contacts. One such section has been illustrated in FIGS. 5a and 5 b.

The next step consists in driving a pointed mandrel or upsetting tool into one of the narrow edges of a knife blade contact in a direction longitudinally of the contact. FIG. 12 shows such a tool including two conical prongs intended to be gang operated. A pair of spaced conical recesses or cavities 3a is formed inside of blade contacts 3 at the two points thereof where the prongs of the pointed mandrels or upsetting tools penetrate into them. At the points where the pointed mandrels penetrate into them the thickness of blade contacts 3 is considerably increased. The points of blade contacts where their thickness is increased are indicated by reference character 3b. Points 3b are formed by short substantially semi-cylindrical ribs 3b. As shown in FIGS. 7a and 7b the terminal caps or ferrules 2 comprise a lateral cylindrical surface 2a and a flat end surface 2b, the latter being provided with an oblong aperture or slot 2c. The geometry of aperture or slot 20 is substantially the same as the geometry of the cross-section of blade contact 3. To be more specific, the aperture or slot 2a is similar to the cross-sectional area of blade contact 3, but slightly larger, thus making it possible to readily insert the end of blade contact 3 remote from its upset or widened edge into slot 2c. There is some play between the edges bounding slot 2c and blade contacts 3 as characteristic of a loose fit. Blade contact 3 may loosely be moved inside of slot 2a until the ribs or lateral projections 3b engage the end surface 2b of terminal cap 2.

The next step consists in driving blade contact 3 under pressure against terminal cap 2. An arrangement for performing this operation is shown in FIG. 10. Cap 2 is inverted and rests with the end surface 2b thereof upon a pair of spaced parallels P. Plunger S is arranged above terminal cap 2 and adapted to drive knife blade contact 3 downwardly until the widened upper edge thereof is substantially flush with the end surface 2b of cap 2. FIG. 10 shows knife blade contact 3 in the limit position thereof reached by unobstructed sliding within the elongated or oblong slot 20. Further downward movement of blade contact 3 requires pressure which is exerted by a downward movement of plunger S. As this downward movement is performed the two ribs 3b swage the end surface 2b of can 2, i.e. they locally increase the width of slot 2c at the points thereof where the thickness of ribs 3b plus the thickness of knife blade contact 2 exceeds the width of slot 20.

In FIG. 8b reference numeral 2d has been applied to indicate the recesses produced in the end surface 2b of cap 2 by penetration into it of ribs 3b of knife blade contacts 3 and concomitant displacement of a portion of the metal of which cap 2 is made transversely to the direction of the movement of plunger S and knife blade contact 3.

The sub-assembly produced by this swaging process can readily be handled, cap 2 and blade contact 3 being firmly joined into a unitary structure. A fine fissure-like gap is formed between the knife blade contact 2 and the terminal cap 2 at the points of the latter where it has not been engaged by widened portions of knife blade contact 3, i.e. where the inner edges of slot 20 are juxtaposed by portions of the knife blade contact 3 which have not been widened by the previous upsetting operation performed with the two-pronged tool shown in FIG. 12. This fissure-like fine gap must now be closed. This is achieved by means of a substantially U-shaped length of wire made of a brazing material such an as appropriate silver alloy. FIGS. 9a and 9b show such a length of brazing material or a brazing pre-form 6 placed upon the end surface 2b of cap 2 around blade contact 3, closely hugging the latter. Thereupon the sub-assembly 2, 3 is placed upon a substantially cylindrical support of a heat resistant inorganic material such as that known as Transite. Such a support with a sub-assembly 2, 3 on it has been in FIG. 11 and reference character T has been applied to indicate the support. While the sub-assembly is on the support T two jets of ignited gas are directed against it, one jet U being directed against knife blade contact 3 and another jet V against terminal cap 2. While jets U, V are impinging upon knife blade contact 3 and upon cap 2 support T is being rotated about the vertical axis thereof. This results in rapid, even heating of sub-assembly 2, 3 and fusion of the brazing pre-form 6. The fused brazing compound of which pre-form 6 is made is attracted by capillary action into the small fissure-like gap formed between cap 2 and knife blade contact 3. Because the mass of the pre-form 3 is small fusion occurs very rapidly. Thus production proceeds very rapidly and there is little danger that the blade contacts become heated to the point where substantial annealing thereof takes place.

It will be apparent from the foregoing that structures embodying this invention include terminal caps of sheet metal whose end surfaces define longitudinal slots having substantially straight portions and portions recessed from said substantially straight portions. Structures embodying this invention further include a blade contact having a rectangular outline formed by a pair of relatively long edges and a pair of relatively short edges. The blade contact is provided on each of the lateral surfaces thereof with ribs projecting progressively away from the plane generally defined by each of said lateral surfaces. These ribs or projections have points of highest elevation at one of the relatively short edges of the blade contact. In other words, these ribs or projections have a progressively increasing height in the direction from one to the other of the relatively short edges of the blade contact, and the ribs or projections have their highest elevation at one of said relatively short edges of the blade contact. The thickness of the blade contact at the edge where the aforementioned ribs are situated varies, being less at points adjacent to the ribs or projections than at the ribs or projections. The end of the blade contact having the aforementioned ribs or projections is inserted into the slot defined in the end surface of the cap. At the points where the ribs or projections of the blade contact are situated the latter engage the edges of the slot and widen the slot and form recesses therein. Narrow gaps are formed between the edges of the slot in the cap and the edge portion of the blade contact recessed behind the ribs or projections thereof. This gap is filled with a body of metal, preferably a brazing compound.

It will be understood that I have illustrated and described herein a preferred embodiment of my invention, and that various alterations may be made in the details of the structure shown and of the process for making the same without departing from the spirit and scope of the invention as defined in the appended claims.

I claim as my invention:

1. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical lateral surface and a fiat end surface, said end surface defining an oblong slot having a pair of longitudinal edges; and

(b) a knife blade contact press-fitted into said slot with one edge thereof, said blade contact being upset at spaced points of said one edge forming spaced points of increased cross-sectional area, said spaced points projecting into corresponding spaced recesses formed in said pair of longitudinal edges of said slot in said end surface of said cap.

2. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical surface and a flat end surface, said end surface defining an oblong slot of predetermined width and said slot having spaced points of increased width; and

(b) a knife blade contact having spaced lateral ribs limited to one edge zone thereof and progressively increasing the thickness of said blade contact at spaced points of said edge zone, the spacing of said ribs of said blade contact being equal to the spacing of said points of increased width of said slot of said end surface of said cap, and said ribs engaging under pressure said spaced points of increased width of said end surface of said cap.

3. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical lateral surface and a flat end surface, said end surface defining an oblong slot having a predetermined Width; and

(b) a knife blade contact fitting loosely into said slot in said end surface of said cap and being upset and locally enlarged only at predetermined points of one edge region thereof to exceed said predetermined width of said slot only at said predetermined points of said edge region, said predetermined points of said edge region being pressed into said slot in said end surface of said cap and being held under lateral pressure therein.

4. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical lateral surface and a flat end surface, said end surface defining an oblong slot having a predetermined width; and

(b) a knife blade contact generally adapted to fit loosely into said slot and being upset at spaced points of an edge thereof to form spaced points of progressively increased blade thickness at said edge, said edge being pressed into said slot in said end surface of said cap thereby establishing spaced points where the width of said slot in said end surface of said cap is increased beyond said predetermined width.

5. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical lateral surface and a flat end surface defining an oblong slot having a pair of longitudinal edges;

(b) a blade contact having a rectangular outline formed by a pair of relatively long edges and by a pair of relatively short edges, said blade contact being provided on each of the lateral surfaces thereof with ribs projecting progressively away from the plane generally defined by each of said lateral surfaces, said ribs being limited to the region of one of said pair of relatively short edges of said blade contact having points of highest elevation at said one of said pair of relatively short edges of said blade contact, and the thickness of said one of said pair of relatively short edges of said blade contact being less at points adjacent said ribs than at said ribs, said one of said pair of relatively short edges of said blade contact being inserted into said oblong slot defined by said end surface of said terminal cap and said ribs being in physical engagement with said pair of longitudinal edges of said slot defined by said end surface of said terminal cap, the portions of said one of said pair of relatively short edges of said blade contact adjacent said ribs and said longitudinal edges of said slot defined by said end surface of said terminal cap forming narrow gaps; and

(c) a body of metal inserted into and filling said gaps.

6. A terminal structure to be mounted on tubular casings of electric fuses comprising in combination:

(a) a terminal cap of sheet metal having a cylindrical lateral surface and a flat end surface defining an oblong slot, said slot including relatively straight edge portions and edge portions recessed behind said relatively straight edge portions;

(b) a blade contact having a rectangular outline formed by a pair of relatively long edges and by a pair of relatively short edges, some of the metal of which said blade contact is made forming projections on each of the lateral surfaces thereof limited to the area of one of said pair of relatively short edges and having a progressively decreasing height in the direction from said one of said pair of relatively short edges of said blade contact toward the other of said pair of relatively short edges of said blade contact, said one of said pair of relatively short edges of said blade contact having portions of relatively smaller thickness adjacent said projections than at said projections, said one of said pair of relatively short edges of said blade contact being inserted into said slot defined by said cap and said projections of said blade contact extending transversely beyond said relatively straight edge portions of said slot defined by said cap into engagement with said edge portions of said slot defined by said cap recessed behind said relatively straight edge portion of said slot defined by said cap, and said portions of relatively smaller thickness of said one of said pair of relatively short edges of said blade contact and said relatively straight portions of said slot defined by said cap forming narrow gaps; and

7 8 (c) a body of brazing-metal inserted into and filling 2,793,269 5/1957 Detch 200-132 said gaps. 2,826,946 3/1958 Calhoun 29-525 2,944,325 7/1960 Clark 29-155.55 References Cited bythe Examiner 2,963,775 12/1960 Chadwick 29-1-5555 UNITED STATES PATENTS 5 1, 3/1920 Trumbull et a1 2 2 BERNARD A. GILHEANY, P77777111}! Exammer. 1,341,401 5/1920 Weisgerber 200-132 WHITMORE WILTZ Examiner- 1,463,038 7/1923 Ellison 200-132 ROBERT W. CHURCH, HIRAM B. GILSON,

2,195,598 4/1940 Olson 29525 Assistant Examiners. 

1. A TERMINAL STRUCTURE TO BE MOUNTED ON TUBULAR CASINGS OF ELECTRIC FUSES COMPRISING IN COMBINATION: (A) A TERMINAL CAP OF SHEET METAL HAVING A CYLINDRICAL LATERAL SURFACE AND A FLAT END SURFACE, SAID END SURFACE DEFINING AN OBLONG SLOT HAVING A PAIR OF LONGITUDINAL EDGES; AND (B) A KNIFE BLADE CONTACT PRESS-FITTED INTO SAID SLOT WITH ONE EDGE THEREOF, SAID BLADE CONTACT BEING UPSET AT SPACED POINTS OF SAID ONE EDGE FORMING SPACED POINTS OF INCREASED CROSS-SECTIONAL AREA, SAID SPACED POINTS PROJECTING INTO CORRESPONDING SPACED RECESSES FORMED IN SAID PAIR OF LONGITUDINAL EDGES OF SAID SLOT IN SAID END SURFACE OF SAID CAP. 